/Engine/Source/Runtime/Slate/Public/Framework/Application/SlateApplication.h
Gets all visible slate windows ordered from back to front based on child hierarchies
void GetAllVisibleWindowsOrdered ( [TArray](API\Runtime\Core\Containers\TArray)< [TSharedRef](API\Runtime\Core\Templates\TSharedRef)< [SWindow](API\Runtime\SlateCore\Widgets\SWindow) > > & OutWindows )